BRISTOL, Va. (AP) _ Virginia-based Alpha Natural Resources is filing for Chapter 11 bankruptcy protection, the fourth big coal producer to do so within the last two years. The company operates about 60 coal mines throughout Virginia, West Virginia, Pennsylvania, Kentucky, and Wyoming. Coal prices have plunged in recent years as utilities have switched increasingly to natural gas, partly because of price, but also because of changing regulations. President Barack Obama on Monday is expected to require even steeper greenhouse gas cuts from U.S. power plants. Alpha Natural Resources Inc. is based in Bristol, Virginia, Rivals Patriot Coal Corp., Walter Energy Inc. and James River Coal Co., have already sought bankruptcy protection.